Telephone or like system



y 2, 1945. c. GILLINGS ETAL 2,37 ,352

TELEPHONE OR LIKE SYSTEM FiledMay 51, 1943 8 Sheets-Sheet l Facy 1.INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE' ATTORNEY TELEPHONE ORLIKE SYSTEM Filed May 31, 1945 8 Sheets-Sheet 2 IN VE N TO R5 CHARLESGILLINGS CHARLES EDMUND BEALE ATTORNEY y 4 c. GlLLlNGS ET AL 2,376,352

TELEPHONE OR LIKE SYSTEM Filed May 31, 1943 8 Sheets-Sheet 3 I I C1 c'nal anb1 cncl c'nd1 CNB CNc CND I 2' lfus CNC r cnbz :r-cna cnbs C1103 I gFif 3' INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE wag ATTORNEY May22, 1945.

c. GILLINGS ET AL 2,376,352 TELEPHONE OR LIKE SYSTEM Filed Ma 31, 1943 8Sheets-Sheet 4 INVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE %Zai4.

AT TORN EY May 22, 1945. c. GILLINGS ET L 6,

TELEPHONE OR LIKE SYSTEM Filed .May 31, 1943 8 Sheets-Sheet 5 YE Fyz YINVENTORS CHARLES GILLINGS CHARLES EDMUND BEALE ATTORNEY May 22, 1945.

C. GILLINGS ET AL TELEPHONE OR LIKE SYSTEM Filed May 31, 1945 8Sheets-Sheet 6 f NI;

,INVENTORS CHARLES GILLINGS C HARLES EDMUND BEALE ATTORNEY y z, 1945. c.GILLINGS ET AL 2,376,352

TELEPHONE OR LIKE SYSTEM Filed May 31, 1943 8 Sheets-Sheet 7 INVENTORSCHARLES GILLINGS CHARLES EDMUND BEALE ATTOR NEY y 1945- c. GILLINGS ETAL 2,37 ,3

TELEPHONE OR LIKE SYSTEM Filed May 51, 1 9415 8 Sheets-Sheet 8 /L $52 "accz cbs Q 2 HI.

1 560cm 12 4 sec of? i t2 cca 9Y I40 ms 01'] seems off i 13 INVENTORSCHARLES GILLI NGS CHARLES EDMUND BEALE ATTO Patented May 22, 1945 UNITEDSTATES PATENT OFFICE TELEPHONE on LIKE SYSTEM Gharles Gillings andCharles Edmund Beale,

Liverpool, England, assignors, by mesne assignments, to AutomaticElectric Laboratories, Inc., a corporation of Delaware Application May31, 1943, Serial No; 489,136

In Great Britain July 28, 1942 a 11 Claims. '(01. 179-48) The presentinvention relates to telephone or like signalling systems and is moreparticularly applicable to the setting and control of automatictelephone switching apparatus over long lines, which may include speechtransmission ther mionic repeaters, by means of voice frequency thechief object of the invention to provide a.

system in which this problem, at least as far as the voice frequencysignalling line is concerned,

is avoided. p

According to one feature of the invention, in

a telephone system suitable for long distance i automatic working andemploying signals of a plurality of voice frequencies for effecting theselective setting of automatic switches over a trunk line, a variablelength train of impulses received from a calling party by equipment atthe outgoing end of the trunk line istransmitted over the trunk line inthe formof a single pulse of substantially constant length comprisingone or more voice frequencies the nature of which varies in accordancewith the number of impulses in the train.

According to another feature of the invention, in a telephone systemsuitable for long distance automatic working and employing signals of aplurality of voice. frequencies for effecting the selective setting ofautomatic switches .over a trunk line, a pulse comprising a plurality offrequencies is transmitted prior to the selective pulses to prepare theequipment for response thereto.

A further feature of the invention is that in a telephone systemsuitable for long distance automatic working and employing signals of aplurality of voice frequencies for effecting the selective setting ofautomatic switches over a trunk line, each train of impulses receivedfrom a calling party by equipment at the outgoing end of the trunk lineis transmitted over the trunk.

line in the form of a code of substantially constant length regardlessof the number of impulses in the train and arrangementsare provided forvarying the interval between codes representing successive impulsetrains dependent on the number of impulses in the preceding train.

The invention will be better understood from the following descriptionof one method of carrying it into effect, reference being had to theaccompanying drawings, comprising Figs. 1-8.

Figs. 1-4 when arranged in the manner indicated in Fig. 3a. show thecircuits of an outgoingmanual-to-automatic relay set which connects overa V. F. signalling line with a distant incoming relay set, the circuitsof which are shown in Figs. 5-8 which should be arranged in the mannershown in Fig. 7a. The local outgoing anddistantincoming relay setstogether provide for V. F."signalling and coded impulsing from anoutgoing trunk line operators position of the sleeve controlled type asalready employed for on demand trunk service.

Before the detailed circuit operations are dealt a with, the method ofworking will be described generally. When the operator plugs into thejack of a free outgoing line equipment, her call ing supervisory lampflickers and a 100 millisecondim. s.) X voice frequency pulse is sentforward to the distant incoming end to seize the associated selector.The operator-now operates the dialling key whereupon the lamp isextinguished and she then dials the required subscribers number which isreceived and stored on uni-selectors at the outgoing end. Each train ofimpulses received is re-transmitted over the line.

in coded digit form involving up to three of four voice frequencies,hereafter referred to as W, X, Y, and Z,-and each coded digittransmittedis preceded by a preparatory signal comprising all four frequencies W-Z,which is effective at the distant exchange to prepare the voicefrequency receiver thereat to receive the coded digit which follows. i

At thedistant end each received coded digit 3 has to be converted backto a train of direct ourrent loop impulses to actuate the switchingapparatus thereat, and the receiving equipment is so arranged that aftera preparatory signal comprising all fourfrequencies together has beenreceived, the digit code following and consisting of not more than threefrequencies W-Z will operate a W, X, Y, Z relay contact pyramid by meansof which the code information can be decoded and converted into amarking on a uniselector for controlling the sending out of acorresponding train of loop impulses.

The second coded digitis transmitted after an interval sufficient tomeet the numerical setting and hunting requirements of the selector andat the terminating end of the line it is decoded as before. Similarremarks apply to the succeeding digits, and when all have been receivedat the distant end, and when the switching equipment thereat has beenset to connect with the required subscriber, the calling operatorwill'receive ringing tone, busy tone, or number unassigned tone todenote the state of the called line. In the mean time, on completing thedialling of the required digits, the operator will have restored thedialling key, and will thus have caused her supervisory lamp to glow.When the called subscriber answers, a Y tone of 200 In. s. length willbe sent back to the originating end to extinguish the supervisory lampand to establish conversational conditions thereat. i

Conversation now takes place, and when'the calling subscriber clears,140 m. s. length pulses of Y tone at spacings of 360 m.- s. are returnedfrom the incoming 'end to the. originating .end 1 and cause theoperators supervisory lamp to glow. When the operator clears by removingthe plug from the outgoing jack, a X tone of 1%2-2 seconds length issent forward to the incoming end, followed by a Y tone of 300m. s.length and the distant equipment is thereupon restored to normal.

Among special arrangements provided according to the present inventionto secure efficient operation is the adjustment of the length of thepause between coded digits transmitted over the line. in accordance withthe. setting up and hunting time required by the distant. selectorswitches. Inthe illustrated embodiment, itis arranged that for thedigits1-5 a predetermined pause is providedwhich will cover the setting up andhunting requirements of digit 5 where the maximum time is involved, andthat for the digits 64} this Paus is, increased to cover therequirements of the greatestv digit 0. By providing pauses betweentransmitted coded digits which will cover the setting up and huntingrequirements of the distant switches in turn, it is possible to avoidproviding storage facilities for more than one digit H at the incomingend of the line as the same storage relays can be repeatedly used foreach digit in. turn, while the adjustable pause arrangement ensures,that this form of digit transmission shall not be unduly extravagant intime.

Considering the operation in detail, when the outgoing operator plugsher cord circuit calling plug into thejack OGJ associated with theoutgoing relay set shown in Figs. 1-4, if the cord circuit speaking keyis thrown, battery via the cord circuitcalling supervisory lampcontrolling relay in the operators position circuit will be extendedover the sleeve of theplug and jack to operate relay M by way of itsleft-hand low resistance winding, whereupon at contacts ml it brings uprelay MM and at contacts 1122, Fig. 4, it steps switch TS from its homeposition to position 1. Relay MM in operating, at its contacts mmZ,connects a flicker earth source via lead ill to the left-hand lowresistance winding of relay 2 lar function at this time but relay FXY atcontacts fryl, Fig. 1, connects X frequency to one winding oftransformer TI, the return path being completed over lead RTN. TheXfrequency is thereupon applied to the outgoing trunk line conductors l4and i5, whereupon at the voice frequency receiver VFR2, Fig. 5,associated with the distant incoming relay set, an X frequencyresponding relay or its equivalent is operated and at contacts 83:!brings up its relief relay XR. Rela XR in operating, at contacts m3,Fig. '7, brings up relay K, which thereupon at contacts lcl locksindependently of relay XR, at contacts k2 prepares a circuit for relayAR in readiness for the termination of the X frequency and at contacts706, Fig. 8, brings up relay PY which how- I ever has no function atthis stage.

At the outgoing end relay FXY at contacts fry 3, Fig. 4, completes aself-driving circuit for switch TS to advance its wipers to position 3,whereupon the circuit of relay FXY is opened at wiper and bank TSi, Fig.2, an d this relaycommences to release slo-wly. Relay on re.- leas ing,at contacts Jmyi, Fig. 1, terminates the sending out of the X frequency,the period of application of which will have been of the order of 100 m.s. as determined by two steps of the switch TS at 20 m. s. per step plusthe m. s. release lag of relay FXY. Relay FXY also at contacts fan/lreconnects a suitable V. F. line termination via resistance YD and atcontacts fxyZ, Fig. 2, brings up relay FC. which thereupon looks overits contacts fcl to earth via bank and wiper T82. Rela F0 also atcontacts'fc2, Fig. 4, advancesthe TS switch to position 4 from which itis t pped. to position 6 over bank and 'wiperfIfSS from an interruptedearth source connected to lead II and delivering 140. m.s.'on, 366 m. s.off, the stepping time therefore being one second.

At the distant incoming end where relay XR has been held operated inresponse to the X fre-. quency and where relays K'and PY areal-so operated, the cessation of the X frequency results in the release of relayXR, whereupon at contacts M3, Fig. '7, earth is extended forward overoperated contacts k2 to bring up relay AR. Relay AR in operating, atcontacts arl, Fig. 6. extends a seizing earth via the winding of relayIR and one winding of the repeating coil RPCZ over'. the

negative wire to the A relay of the selector switch associated with theincoming relay set. The selector A relay and relay IR operate in seriesand the former prepares the selector for receiving direct current loopimpulses from the incoming relay set, while the latter at contacts irl,Fig. '7, [brings up relayv NN and at contacts irZ, Fig. 8, holds relayPY independently of relay K. Relay N has mainly a preparatory functionat this stagebut contacts not, Fig. 6, provide a shunt path roundcontacts art of rela AR. f

No further circuit operations occur at either end of the, trunk lineuntil the operator'throws her position dialling key, whereupon batteryis extended forward from the position over the cord tip and ringconductors and a high resistance is introduced into the sleeve circuitto extinguish the calling supervisory lamp. The battery over the tipconductor brings up relay RR. Fig. l. and this relay in operating, atcontacts m l brings up relay AM, whereupon at contacts aml, Fig. 4,earthis extended to operaterelay B, Fig. 2. Relay B in, operating, atcontacts, b2 and b3,

' 1, connects relay AM to thetip and ring conductors so, that this relaynow holds over its upper winding independently of relayjRR,

the circuit of whichis disconnected at contacts b4 so that it releasesafter a short interval. At contacts b the flicker earth circuitisfopened cuit but owing to the high resistance whichhas been includedinthis circuit in response to the operation of the dialling key,relay'KRwill not operate though relay M remains held.

and relay KR is introduced into the sleeve cir- The operator now dialsthe first digitof the required number; and when the dial is movedoff-normal, the battery connection to the tip and ring conductors at theoperators position is removedand these conductors are now; loopedtogether. over the dial impulsing springs so that 3 relay AM is nowheldenergised over both its windings in series. On the first interruptionofthe impulsing circuit, relay AM in releasing-at contacts aml, Fig.4,extends earth over contacts .bl and low resistance winding of relay C,wiper and bank DDZ of the digit distributor switch DD to the magnet DSAMof digit switch DSA, while on the subsequent re-operationof relay A themagnet is de-energised to advance its wipers to position 1. If the digit5 is dialled, the DSA switch wipers will be advanced to position.5.RelaysB andC hold operated during the train and contactsicz en'ergisethe magnet DDM out, the leads representing these frequencieswillof.1th.e .digitdistributor switch DD during this time. On the release ofrelay C at the end of the train, magnet DDM is dc-energised and advancesthe DD switch wipers to position 1, while at contacts cl Fig. 3, earthiseXtended via'corltacts anal and wiper DSA2 in position 5 to operaterelays .CNA and CNR in series. Relay CNA in operating,-at .lts contactscna l locks itself over wiper and bankDSAZ independently of the contactscl, at contacts cnaZ prepares a"fur DSB, DSC (not shown) and to digitswitch s1),

reception of digits onthese switches bringing up the associated relaysCNB, CNC and CND, Fig. 3. Immediately the first dialled impulse trainhas been completely received as indicated by the operation'of relay CNR,sending out ofthe corresponding V. F. coded digit over trunk line l4, l5isinitiated. Onthe operation of relayCNR,

contacts cnrl step. switch SC oif-normal, where-.

upon it operates relay ST by way of both its windings in series withmagnet SCM which cannot. operate in this circuit. Relay ST thereupon atcontacts stl short-circuits its left-hand high resistance winding,whereupon magnet SC-M is operated and switch SC self-drives to position4 where the holding: circuit for relay ST is opened and this relaycommences to release. 'During the operated. time of relay ST, contactsst2-st5,

1, apply all four. frequencies W-Z to the trunlr line by way oftransformer TI to provide the preparatory signal which precedes thetransmission of each: codeddigit, while contacts st6, Fig. 2, disablethe V. F. receiver VFRI associated with the outgoing relay set. on therelease of relay ST, contacts .stl, Fig. 3, operate relay. S'oyer bothits windings and bank and a 3 wiper SC'lin series'with'magnetSCM'andwhen relay S operates and at its contacts sl] shortcircuits itsleft-hand high resistance winding,

SWitCh SC will commence'to self-drive to position 9', Relay ST inreleasing disconnects the four-frequency signalling circuit and relay Sin operating, at contactss4, Fig. 1, connects up to line a frequencycombination in accordance with the digit dialled as controlled by theDSA switch banks DSA3-DSA6 which connect up with contacts 34 overoperated contacts cna4 and resting contacts 273. i

The proposedlV. F. digit code is as. follows:

Code Digit one 1 -Inresponse to the dialling-ofdigit 5.17118 DSA switchwipers will have been set to position 5, andinorder that in thisinstance a coded digit comprising frequencies W and Z may be sent bewired up to contacts ,5 on banks .DSA3 and DSA6,the contacts 5 on banksBSA-4 and DSA5 beinglleft unwired. On the operation of relay S followingthe release of ,relay ST, the four prepare frequencies W-Z willtherefore be replaced by the two frequencies W and Z.

Thesending out of thetwo frequencies W and Z continues until the switchSC reaches position 9 where the circuit of relay S is opened. In thisposition during the slow release of relay S, relay ZR operates over itslower high resistance wind ing in series with magnet SCM whichis inoperative owing to the high resistance of relay ZR.

Relay ZR thereupon at contacts zrl completes a homing circuit for thedigit switch DSA y ia its upper low resistance winding, contacts cnal5and wiper and bank DSAl, at contacts 272 completes a locking circuit forrelays CNA and CNR in series and relay CNR will also. release if nofurther digits have yet been dialled. I

If bythis time the operator has completed the dialling of the seconddigit, which willbe assumed to be 8, relay CNB will have been operatedinseries with relay CNR and consequently with relay CNR still held,switch SC on reaching its home position will commence another cycle ofopera tion. Relay ST is again operated and functions in the same manneras before to send the prepare pulse and is followed by relay S tosendout the code corresponding to digit 8 which is The SC switch onadvancingto contact 9 ter- "minates the sending out of the W, X and Yfrequencies corresponding to digit 8 by. operating relay ZR whichproceeds to home the DSB switch, the homing circuit extending in thiscase via the upper low resistance winding of relay ZR,.resting contactscnafi and operated contacts cnb5 and bank and wiper DSBI. This isfollowed by the homing of switch SC, whereupon the equipment position 9.

will be ready to send out the next received impulse train-in codedvform.

The interdigital pause is "partly determinedby the bathing time of thedigit switch controlling the coded digit which has just been sent out,the time concerned being the homing time from the position to which thisswitch has been set by diallingplus the homing time of switch S fromThis arrangement provides a suitable interdigital pause for-digits up to5. In the case of digits 6-0 this time would be slightly less and infact a longer time is required to cover the correct functioning of theswitches at the distant end. This is taken care of by arranging tooperate a relay EP, Fig. 3, when relay S operates to initiate thesending out of a coded digit of a value from 6-0. For instance whenrelay S operates to initiate the sending out of the frequencies W, X andY corresponding to the second dialled digit 8, on the operation of relayS, (3011-. tacts s3 complete a circuit to operate relay EP from earthedoperated contacts cnb'l, wiper D832 of the first digit 5, or thereduction 'tO-f'PEQIZEHe cies W, X and Y in the case of the second digit8, the short-circuit will be removedfifrom relay CB which now operates.Relay CE in operating, at

- its contacts 0124 and cbl, .Fig. 5, completes holdon contact 8,operated contacts cnb3, normal I contacts cnall, operated contacts s3 tobattery via the winding of relay EP. In this instance relay CNB willhave'been operated byway of its right handwinding, the .left handwinding only being used for digits up to 5. Relay EP in operating, atits contacts epl locks itself independently of relay S and at itscontacts e123 ,(not shown, but assumed to be located in Fig. 4 andconnecting the home contact of bank DSBI with the other contacts)preparesfor the provision of an extra pause after the second digit 8concerned, the other contacts ep2, ep' l and ep5 serving simifllarly'iorproviding an extra pause if required,

after the first, third and fourth digits respectivelypy y When switchDSB restores to its home position after the sending out of the codeddigit 8, since relay EP is operatedat this time the switch Wipers areagain advanced to position 1 from which the switch continues to rotatethrough another full cycle. 'During this time'relay ZR will bemaintained operated and will maintain relays CNB and CNR from earth overcontacts 2T2, cnaZ, cn-b-Zleft-hand winding of relay CNB to battery viarelay'CNR. .While switch D83 is stepping to position 6, the holdingcircuit for relay EP will be opened. at bank and wiper D832 and thisrelay will release during this time so that when switch DSB'reachesposition 6 relay EP will be unable to re-operatej Hence when the switchDSB reaches the home position on the additional cycle, since relay EPwill now be nor mal, there will be no circuit to step it on from itshomeposition and relay ZR will therefore release. 7 Relay ZR inreleasing homes the SC 'switchand releases relay CNB. ,The SC switch onreaching its home position waits until the next digit has been received,or, as before described, continues another cycle if this .has alreadybeen received,

- Considering now the reception of the coded V. F. digitsat the incomingend, the WXYZ .prepare signal which precedes each digit operates allfour relays Wit-ZR, Fig. 5, contacts of which bring up relay CA, Fig. 6.It. will be remembered that at this incoming end relays K, PY, AR, IRandNN are operated as a result of the seizure of the trunk line. On theoperation of relay XR, relay AR, Fig. V7, is released but withouteflect, while on the operation of relay CA, contacts cal,

prepare an operating circuit for relay CB ing circuits for relays WR.and ZR which are-op erated in response to thecoded digit frequencies Wand Z where digit 5 is involved, so that on the cessation of thesefrequencies, relays WR' an'd ZR will remain held. Other contacts ofthese re-' lays which are, not shown are arranged "in' a known pyramidformation so as to setup aIsuitable marking over the fifth otthe tenleads 14), Fig. 8, to contact 6 of the bank SS2 0f the sender switchSSso as to control the sending out ofa number of direct current loopimpulses correspondingto the V. F. coded digit 5 concerned.

Relay CB also at contacts 0225, Fig. 7, brings up relays Pand C. Relay Cin operating, at contacts cl bringsup relays CC and GY and at contactsc2 and 03, Fig. 6,-releases relay IR and loops the outgoing negative andpositive leads via the impulse sending circuit which involves the motora driven loop impulsing contact springs IMPI;

to! connects these springs to magnet SSM. 0h

at present short-circuited by Wiper SS! in its home position. Relay P inoperating looks over its contacts pl and at .its contacts p5, Fig. 8,operates relay CK, contacts old and 0703, Fig. '5,

of which serve to'terminate the trunk line 'via resistance YE whi1e loopimpulses are subse-' quently' transmitted from the incoming relay set.Relay GY has no direct function at this stage but relay CO in operating;'at'its conta'cts'cc'l, Fig. 8, connects earth to the motor driven magnet impulse springs IM'PZ.

The impulse springs IMPI and IMP2a're' operated ten times persecond,"the former being closedfor 33 of. the period of each impulse andthe latter being closed for the remaining 66% of the period. If on theoperation of relay CO the impulse springs IMPZ are open, or if not, whenthey next open',,relay IG operates and at contacts the next closure ofthe springs IIMPZ, magnet SSM is energised and on the next opening,magnet SSM is de-energised and advances the SS wipers to position 1. Atthis point the loop impulse springs IMPI are closed, so that whensprings IMPZ again close to re-energise 'magnet SSM, springs IMPIin'opening produce tion of the first output impulse. On the next openingof springs IMPZ, the SS switch wipers are advanced to position 2 whilesprings-IMPI nowclose to terminate the break portion of the first outputimpulse. During the stepping fromposition 2 to position 3 the secondimpulse is sent out and so on until five impulses have been sent outcorresponding to, the received V. F.'coded digit. Wiper SS2 on reachingposition 6 at this time will encounter an earth marking which will becon-- nected thereto over} contacts'of relays WR and ZR. within theknown pyramid arrangement. Re

lay SZ thereupon operates and looks over its contacts sel, while atcontacts s22 it short-circuits the loop impulse springs IMPI to preventfurvther impulses being sent out'to the first selector, and at contactss23 it releases relays CB and CA. In response to the train of five loopimpulses, the first selector is stepped up to level fi and then-proceedsto perform an automatic rotary the break porhuntingioperation to find asucceeding selector infltheselected group. Relay GB in releasing, atcontacts c114 and cbl releases relays WR and ZR, atcontactscbBre-operates relayAR over contacts ca.2 and yr3 and opens the circuitof relayC, andat contacts cbfi it releases relay 1G whereupon-the SSswitch self-drives to its home position relay SZ remaining locked tobank and wiper SS3 during this time. When switch SS3 reachesiitshomeposition, relay SZ releases and re-preparestacircuit for relay CB. .011the re. lease of relay after its slow period, relay CC, is released andrelay GY commences to release slowly an d the repeating coil RPC2 is recon nected to the outgoing negative and positive leacls so that relay IRre-operates. Relay CK, Fig. 8, is connected upfoverlead 12 to aninterrupted earthsourcewhich gives one second pulses at four secondintervals and therefore slowly, pulses but without e'fiect" at thisstage except under specialtonditions when busy tone is returned from"the selector as described later. With relays PY, NN, P, AR and IR heldand with relay CK pulsing, the incoming end is now ready ta receive afurther set of frequencies corresponding to the next dialled digit 8,which will be transmitted from the outgoing end after the pulseformtbset up the selector trainto the required subscriber.

I At the outgoing end, where relays M, CO',

FC, AM and Bar held operated, the operator after, dialling the requireddigits will restore her diallingkey, whereupon a comparatively lowresistance battery potential is momentarily applied whereitis furtherslowly interruptedby contacts cm and 0763 though withoutany particularpurpose in thisinstance. The tone then extends back tothe outgoing relayset where it finds a circuit to the outgoing operator'via transformerTl, the singleway orso-called stopper valve SV and repeating coil RPCLTheprimary function of valve. SV, is l to prevent transmission from athe cord circuit to the trunkfl line so as to prevent noise or'the likeat the outgoing end switching the linefecho. suppressors against thepassage of tonesand signals from the distant incoming end. At theincoming end, during the transmission of ringing tone, relays K, AR, PY,NN, IR and P continue to be held operated, while relay CK continues'tobeslowly pulsedL j 1 When the called subscriber answers, the linebattery feed to the calling side of the final se:

lector circuit is reversed and the battery applied to the positivelineoperatesrelay I, while'relay IR releases. Relay Lin operating, atcontacts il,

Iiigflf, releasesrelay K and this relay' atcontacts k3 bringswup'relayGX,lwhile at contacts k6, Fig. 8, th'ejcircuit of relay PY isopened. During the release time of relay PY relay FY is broughtji ipover' contacts 272 kt and p213 and, at contacts {31] steadilyYenergisesrelay CK which up to now has been pulsing. Relay PY'in releasing opensthe circuits or relays FY and 0 and during thereleas'e time of these tworelays a200 m. s. Y frequency subscriber answerf signal is sentfback totheoutgoing end to dim the op'erators calling supervisory lamp andtocomplete the conversa at the operator's position circuit to the sleeveof the calling plug and this battery extendsover jackOGJ to bring uprelay KR. Relay KR thereupon at contacts l crz prepares for called partysupervision, at contacts krl removes the battery feed for relay AM whichremains held on its upper winding to battery applied to the tip and ringconductors in the position circuit and at contacts Fort provides a locallocking circuit for relay KR After the momentary applicationofresistance battery to the sleeve circuit, the high resistanceoriginally introduced into this circuit on operation of the dialling keyis short-circuited, while ashortinterval later the battery applied tothe tip and ring'condu'ctors in the position circuit is removed and,relay AM releases. On the reticnalconditions thereat.

,'At the outgoing end relays M, MM, KR, CO and PC are held operated atthis time and "the TS switch isin positiont. On receipt of the Yfrequency, this extendsover transformer T2 into theV.1F. receiver VFRIand brings up a Y relay or its equivalentcontacts'yl of which bring uprelay RS. Relay BS in operating, at contacts rsl prepares a circuit forrelay R D, and at can. tacts r82 operates relaySA which thereupon atcontacts sal brings up relay, CT and at contacts sa2locks via bank andwiperjTS2. Relay CT in operating, at contacts ctZ, Fig. 1, appliesbattery via resistance, YC to the ring, conductor for throughsupervision purposes in cases wherethe outgoing operators position. isserving in an in:

terme'diate capacity between a calling and ,a

. called exchange, at contacts ct3 disconnects the sultant release ofrelay B after its slow period,

contacts I connect earth over contacts ctZi, Icri, b5 and mmZ, and theleft-hand low resistan ce winding of relay M to the sleeve circuit soasfag'ainto bring about the lighting r the calling supervisory lamp.This condition persists until the called; subscriber answers.

Meanwhile, the 'selector train at the distant exchange will haveconnected with the required subscriber and if he is free, the finalselector will return the interrupted ringing tone back over the speakingconductors to the incoming relay 'set,

earth appliedtothe sleeve circuitso asto enmguish the callingsupervisory lamp, and at con? tacts cit and 0155 establishes throughconversational conditions at the outgoing end. At the conclusion of theY frequency pulse, relay RS commences to release slowly and during thistime relay RD operates and maintains relay CIHover contacts 1111' andctl. when relay "Rs releas s, relay RD slowly releases in' turn, relayCT now remaining held to earth via contactssal and bank andWipe'rTSLQ fH Conversation nowproceeds between the calling and' called parties,relays AR, NN, I, P, and GK being held operated-at the incoming end. Atits conclusion'the called party. on hanging up brings about restorationtolunormal of the line feeding battery potentialat the final selector,whereupon relay IR again operates and relayI releases, results in thetransmission of a clearing signal comprising llO m. s. pulses of Yfrequency at spacings of 360 in. s. back to the outgoing endto eifectthe lighting of the outgoing operatorslsu pervisory 8 ml Relay I inreleasing, atlcontacts iZ liig; 8, brings-up relay OK and this relay atcontacts clcl connects up a 14.0 m. s. on, 360' m. s. ofl' earth sourceover lead B to relay FY, whereupon at contacts i1 2, Fig. 5, 140 m. s.pulses of Y frequency are returned over the trunk line con- At theoutgoing end where relaysM, MM, CO, FC, KR, SA and CT are held operated,the first Y pulse brings up relay RS and the first off period brings uprelay RD during the slow release period of relay RS and relayDRmaintains relay CT. When'the next Y pulse arrives, relay RD will notyetihave released due to the combined release times of this relay andrelay RS being longer than the 360m. s. off period so that the holdingcircuit for relay CT which has been previously maintained overcontactsrd l,'ct|,' 3 1, $156 andsS to earth is nowopened at contacts y! andrelay CT now releases; Relay RS operates on this and" subsequent Yfrequency pulses and relay RD remain steadily operated since it isenergisedduring the release time of relay Rs duringeach interval andremains hel'd due to itsslug during each impulse. n the release ofrelay" CT, the conversational condition atthe outgoingend is broken downat contacts @154 and ct5 and at contacts ct3 earth is extended forwardover the sleeve circuit to give the clearing'signal to the operator bylighting the-calling supervisory lamp.

Thereason for arranging the'circuit to require two pulses to give therequired control is to prevent simulation of the clearing signal byspeech.

On receipt of the clearing signal, the operator will withdraw hercalling plug from jack OGJ' and relay M thereupon releases, whereuponrelay MM commences to release slowly; The otherrelays SA, CO, F'C'remain held to bank and wiper TSZ, relay CO, on the release of relay MM;main taining an engaged test battery via resistance YB on the sleeveofj'ack OGJ. Relay MM also releases relay KR. Relay M at contactsmZFi'g. 4; causes the TS switch to advance'to position 7 from whichearth over contacts sa4 "causes'it to self-drive to position whereits'driving circuit is opened at bank TS4. During thistime relay B, Fig;2, is operated over bank. and, wiper TSI. when switch TS reaches contactI5, it proceeds to advance onward" to position 19 under control of a140' ms. on, 360' m; s, olfinterrupted' earth supply connected to leadI'l whichextends to magnet TSM viabank and' wiper TS3. When position I9is reached; relay B has its circuit opened and commences to releaseslowly, while relay FXY is now operatedlj' This operation of relays B-and in turn serves to send forward a clear down? signal comprising, a 1%second pulse of X frequencyfoll'owed bya 300 m. 's."pul'se of Yfrequency, 'It will be seen from Fig. 1 that relay B in operating, atcontacts b6 extends X frequency over contacts mm l; st2', fxyl andresistance YD to the winding] of transformer Tl from whence-it extendsto line. This, circuit is maintained until relay FXY operates and opensthe)! frequency circuit at contacts ,frtyl, the time being determined bythe stepping of switch TS from position I to position 19. On' theoperation of relay FXY, contacts ,fwy'l connect Y- frequency toline. Onthe release of relay B after its, 'slow period, a self-interrupteddriving circuit is completed for switch TS at'contacts b8 and the switchthereupon advances itswipers to position '20., The circuit for relay FXYis now broken .atba'nk. and wiper TS-l andafterthe slow" release periodof I this relay; the transmission of the Y frequency to-line-'isterminatedi Itmay be mentioned-here that the X frequency pulse willhave-forced the line echo suppressors to change round infavour offorward sen'dingfrom the'out'going end, so that during this time relaysRs and-RD will have re-;

' position 24, it will remain there until both relays- RS and RD restorewhen contacts rs4 and rd! will allow the switch to step on to itshome-position. In this position-relays- SA, FC and CO which have beenheld operated from wiper and bank T82 are released and the outgoingrelay set is ready to deal with further calls.

At the incoming end, theposition is thatrelays AR, NN', P; IR, or: and(so; are held operated while relay FY is pulsing; .On receipt of the Xfrequency which will occur during the silent period of the Y' clearingsignal being sent fromthe' incoming end, relay XR- operates and at itscontacts m3, Fig. '7, operates-relay GY which disconnects the pulsingcircuit of relay FY and so terminates the sendingoftheY pulses, while atthe same contacts the circuit of relay GX is opened so that it commencesto release slowly. On the release of relayGXrel'ay CC is operated andthe equipment now awaits the Y frequency from the outgoing end;On'receipt of this frequency, relay YR in operating, at contacts 3 1'3brings uprelay CR. This relay atcontacts er: operates relay 0 and atcontacts crl locks itself and disconnects relay NN which commences torelease slowly. Relay C -in operating releases relays IR and AR; so thatwhen relay NN releases, the forward holding loop to the selector trainis opened and this train. now restores to normal. Relay NN- inrel'easingalsoreleases relays P, CC, GY and C and on therelease of relays P andCC, relay CR releases. frequency,v relay YR releases and the incomingequipment is ready-for further use.

c The primary function of'rela-ys GK and" GY at the incoming end is toprevent false operation due to components of speech simulating the X andY signalling frequencies and the arrangements are such that afalse Xfrequency followed by a false Y frequency will be ineffective unless thefalse X frequency is of at least 300* milli' seconds duration. It willbe appreciated that the possibility of a false X frequency of at least300 milli seconds immediatelyfollowed by a false Y frequency isextremely remote. During conversa tion the operation of the supervisoryrelay I'will have restored relay K tonormal so that if a component ofspeech during this time simulates the X frequency, relay GX will startto release slowly owing to the operation of relayXR). Only if thecomponent is sufiiciently long, i. e., above 300 milli-seconds duration,will relay GX be released and relay CC operated, andthe connection willonly be releasedif a; false'Y signal follows immediately so asto operaterelay CR.

Assuming now that the outgoing operator clears in face of numberunassigned tone or if the called subscriber fails to :answer, in "orderto be sure of clearing, down the distant incoming equipmentparticularlyin face of number unassigned tone which may be, appliedcontinuously for 4 seconds, it is arranged that the X frequency of theclear down signal is lengthened to a p'eriod of, the order of 6 seconds,thisfrequencyfbeing followed by the usual300 m. s. .Yffrequency,'v

Onthe withdrawal of the plug, relays On the terminationof the relay GXreleases, relay CC operates.

and KRrelease as before. Relay M in releasing causes the TS switch toadvance to position 7, but in this instancesince relay SA has not beenoperated owing to non-receipt of a subscriber answer signal, the switchTS will not new selfdrive to position .15 as before, but insteadwilladvance step by step from the. interrupted earth supply on lead H tothis position from which it will again advance under control of the sameearth supply to position 19 as before. i From position 19 theswitchmoveson .to its home position as already described. During the steppingfrom position '7 to position 19rel'ay B is operated to send out Xfrequency as before, but. in this instance the increased stepping timeof switch TS gives approximately a fi-second period of transmission of Xfrequency. The 3007111. s. Y frequency then follows in themanner alreadydescribed.

At the incoming end relays K, AR, NN, PY,

P and IR will be in operated condition and relay CK will be being slowlypulsed. The reception of the X frequency results in the operation ofrelays XR, C, CC and CY in turn. Relay C in operating causes the steadyoperation of relay CK, releases relay; IR and transfers the selectorholding loop to wiper and bank SSI. The receipt of the Y frequencybrings up relays YR and CR, whereupon relays K, NN, CK, C,,CC, PY, P andCR are released and the loop to theselector train is broken. At the.termination of the Y frequency, relay YR releases and the incomingequipment isrestored to normal.

In case busy tone is returned from the final selector, or a precedingselector, the circuit operations at the outgoing end are the same asdescribed for the number unassigned or ringing tone, but at the incomingend beforereception of the clearing signal, relay I will beimpulsed fromthe busy flash battery applied atthe selector in addition to the relaysheld as already mentioned. The first full operation of relay I re leasesrelay K which cannot re-operate and relay K in releasing operates relayGK and opens the slow pulsing circuit for relay CK so that this relaynow remains normal. The busy tone now extends through without furtherinterruption from the final selector to the operator, the interruptionat the incoming relay set being unnecessary with busy tone as the echosuppressors can readily restore during the silent periods.

When the operator subsequently withdraws her plug, the G-second X, 300m. s. Y frequency clear down signal is now sent forward asdescribed.

At the incoming end relay XR responds to the X frequency and brings inrelay GY, while when In response to the Y frequency relay YR brings uprelayCR which operates relay C and also releases relay NN whichdisconnects the circuits of relays C, CC, CR, P and GY. The operation ofrelay C releases relays IR and AR and relays AR and ,NN initiate therelease of the selector train so that on the release of relay YR at theend of the Y frequency, the equipment will be 7 quired to select anoutgoing V. F. trunk to a further exchange, when the tandem selector Cilchange.

five battery applied tolthe test lead P will be returned to the tandemincoming relay set to provide a through .path from the incoming relaysetto the selected tandem outgoing relayset in 1 order to allow thesubsequent coded digits to extend. straight throughto the terminatingex- Referring now to Fig. 6,if after the transmission ofthe appropriatenumber of trains of loop impulsesa positive battery is applied to thetestylead P at the tandem outgoing relay set taken into use, relay DCOoperates. and. at its contacts dcol cuts off any further circuit forrelay CB and at the, same contacts completes a locking circuit foritself. At this time relays K, PY, AR, NN, IR, and P will be operatedandrelay CK will be pulsing, whilerelays CA, 2GB and C will be normal.ates, at contactsdcoa it opens the circuitof :relay K, and on release vofthis relay contacts k3 connectup relay GK and ,contactslc5 releaserelay CK. Thereupon atcontactsckZ and'ck3 the incoming trunk conductors.and 15 are extended" through via repeating coil RPCZ and the tandemselector train to the tandem outgoing relay set taken in use. Hencereceived codedV. F. signalsv corresponding'tothe subsequent digitsdialled will extend straight through to the-tandemoutgoing equipmentwithout having been operative at the incoming equipment since as relay.03. cannot be operated, the digits are not stored and no eircuit iscompleted for stepping, the switch SS. The coded V. F. signalsaccordingly extend through the tandem outgoing equipment and, out

incoming V. F. trunk as described. above, however, no conversion will benecessary asthe digitalinformation will already be in V. F. coded form,To enable the tandemoutgoingrelay set to meet these two requirements asuitable discriminative method ofseizureis utilised, seizure in theformer case where conversion is required being. characterised by adirect current loop train has been set up, an outgoing DC/VFrelay acrossboth legs of the incoming line, while seiz ure in. the latter case whereconversion is not required will be characterised by a balanced earthconnection on to both legs of, the line via the relays I and IR inthentandem incoming relay set concerned.

In the system just desc ranged to precede each coded V. F; digit by apreparatory signal comprising all the signalling A frequencies ,incombination. One function of this is to ensure that the line echosuppressor is switched inthe, right direction in readiness for thefollowing coded digit and so to prevent clipping thereof, andanotherfunction is'to exercise the incoming voice frequency signal receiven. Anadvantage of this arrangement is that unless all the frequencyresponsive relays in the incoming voice frequency receiver functioncorrectly, it will be impossible to send out trains of impulses andhence the sending out of incorrect digits due to partially storedfrequency codes is prevented. Further-more if on seizure of a selectorby the When relay ,DCQ oper 9 "bed it has been ar incoming equipment;transients of the order of the dialing frequencies. are encountered,these might. be stored by the incoming voice frequency receiver and sentoutin corresponding impulse forms With the illustrated arrangementshowever, this trouble is avoided since the incoming equipment is notproperly responsive unttlsafter a prepare signal has been received.Though it ispossible to avoid trouble due .to signal clipping by theecho suppressor by making each coded d'igit or su-fficien't duration asto be substantially.

unaffected thereby, the other troubles which arise when the preparesignal is not utilised would still'obtain and the arrangement describedtherefore adds appreciably to the reliability of the system;

What we claim as new and desire to secure by Letters Patent is l 1. Inatelephone system, a trunk line, aresponsive device, means in the trunkline responsive to different length series of impulses received from-acalling party for transmitting over the frequencies in said singleimpulse varying in accordance with the number of impulses in said re?ceived series.

3. In atelephone system, a trunk line, a plu- 1 tion of the switches. v

rality of "automatic switches accessible thereto,

means associated with the trunk line for transmitting' an impulse ofcurrentthereover compris ing a plurality of voice frequencies beforeeach switch is. operated and means for thentransmitting another impulsecomprising a lesser number of said voice frequencies'to the switches tooperate the same, the number of voice frequenciesi in theseco'ndfimpulse varying in accordance with the, operations required in each ofsaid automatic switches.

4. In. a telephone system, automatic switches, "a register, means fortransmitting series of impulses" to said register to variably operatethe the time interval between transmitted impulses representing receivedseriesof impulses, depend: ent on the number of impulses in thepreceding series. v

'Z. In a telephone system, a trunk line, auto matic switches, means forsimultaneously transmitting a plurality of voice frequencies to saidautomatic switches to. extend a connection over said trunk line andmeans for transmitting a supervisory signal back over thev trunk lineafter the connection is extended comprising a single one of the voicefrequencies used in the opera- 8'. In a telephone system, a trunk line,an automatic switch, a plurality of sources of-"alter nating current ofdifierent frequencies, means of connecting one of said sources to saidtrunk line to seize said switch, means for simultaneously connecting allof said sources to the trunk line to prepare the switch for operation,and means for simultaneously connecting particular combinations of saidsources to the trunk line" to selectively operate the switch to extend aconnection. 9. In a signal system, two control offices having aninterconnecting line, a plurality of sources of signalling current eachsource having different electrical characteristics than the othersources, devices in one of saidoflicessaid devices respon sive to aplurality of received signals for transmi tting said signals over theline by meansof' a signal of substantially constant length'includinga'code impulse of current from all ofsaid sources, a receiving device atthe other office responsive to said code, and means controlled by saidreceiving device to translate the code to signals corresponding tosaidreceivedsignals;

1-0'. In a telephone system, a trunk line connecting two exchanges, aplurality of frequencies of alternating current, aplurality of automaticswitches successively controlled by received'impulses to select aplurality of particular combinations of said frequencies, means forsuccessively controllingeach of the switches connected tosaid particularfrequencies to individually apply to said line a signal including a codepulse of the selected frequencies, the interval between the same, meansin the register, for simultaneously transmitting a, plurality of voicefrequencies to operatethe switches, each plurality of'voice frequenciessimultaneously transmitted varying in composition in accordance with thenumber of impulses in the series registered.

'5. In a telephone system as set forth'in claim 4 in which there ismeans in the registerior delaying, the time of transmission of" thevoice frequencies corresponding to a series of impulses for a timeperiod. varying in accordance :with the number of impulses in the seriesregistered.

6. In a telephone. system, a register, means in the register responsiveto a plurality of received series of impulses for transmitting animpulse of substantially constant length foreach series received',regardless of the number of impulses in the series, and means in. theregister for varying connection of each of the successive signals controlled by the switch that applied the'precedi-ng code, a deviceresponsive to said code signals; other automatic switches, and meanscontrolled by said-responsive device to operate said other switches bypulses corresponding to the received impulses used to operate each ofsaid first automatic switches to select the connected frequen cies.

11. In a telephone system, a toll line terminating on a deviceresponsive to particular voice frequencies for controlling switches fromreceived digital information, means for transmitting over said lineparticular digital information as a voice frequency signal of constantlength comprising a preliminary portion of said voice frequencies toprepare the device on said: line for the. digital portion comprising alesser number of said frequencies for operating the switches.

CHARLES GILLINGS. I I CHARLES EDMUND BEALE,

